1. Field of the Invention
The present invention generally relates to zoom optical systems that are used for photographing cameras and in particular in lens shutter cameras, and cameras equipped with such a zoom optical system.
2. Description of Related Art
In recent years, lens shutter cameras equipped with a zoom lens have become popular. In particular, cameras with a zoom ratio of 3 or greater are desired by the users.
Also, even though lens shutter cameras may have photographing lenses with a high zoom ratio, the cameras are desired to be small and light. For this reason, reduction of the diameter of lenses and the total length of lenses in the optical system has become an important objective for miniaturization of cameras.
To achieve such an object, optical systems of a variety of types have conventionally been proposed. Among those optical systems, optical systems of the type that can achieve miniaturization with a relatively simple structure and that have been proposed include a zoom optical system equipped with three moveable lens units, which is composed of a first lens unit with positive refractive power, a second lens unit with positive refractive power and a third lens unit with negative refractive power.
Although the conventional zoom optical systems have a relatively small telephoto ratio of about 0.8, the total length of the lens system at a wide-angle position is large. Accordingly, the diameter of the first lens unit and the third lens unit is large, and therefore they are not suitable for miniaturization of cameras.
Also, in the aforementioned zoom optical systems, an aperture stop is disposed within the second lens unit. As a result, the zoom optical systems may be substantially affected by decentration of each of the lens components among which the aperture stop is placed.
Furthermore, since the aforementioned zoom optical systems need a plurality of lens barrels among which a shutter is placed, large errors would occur in assembling the optical systems. Accordingly, there are problems in that deteriorations of the performance would likely occur.
Among the aforementioned conventional zoom optical systems, an attempt is made to achieve the size reduction and reduction of the number of lenses by effectively utilizing aspherical surfaces and reducing the number of lenses in the second lens unit with positive refractive power. However, while the number of lenses in the second lens unit may be reduced, the aspherical surfaces alone cannot sufficiently correct the aberration in the second lens unit, such that the influences of decentration of lens components in the second lend unit become greater. Furthermore, the first lens unit is designed to generate aberration in order to compensate for the influence. Accordingly, the influences of decentration of lens components in the first lens unit and the second lens unit become greater. Consequently, there are problems in that deteriorations of the performance due to errors in assembly would become greater.
The present invention has been made in view of the problems described above.
In accordance with an aspect of the present invention, a zoom optical system comprises, in order from an object side: a first lens unit having positive refractive power; a second lens unit having positive refractive power; and a third lens unit having negative refractive power, wherein a magnification is changed from a wide-angle position to a telephoto position by moving the lens units toward the object side so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, and wherein the zoom optical system satisfies the following conditions:
0.5 less than LT/fT less than 0.8
0.5 less than fG1/fW less than 1.45
0.8 less than fG2/fW less than 1.2
0.4 less than |fG3/fW| less than 0.5
where a reference symbol fW represents a focal length of the zoom optical system at the wide-angle position, a reference symbol fT represents a focal length of the zoom optical system at the telephoto position, a reference symbol LT represents a distance as measured from a most object side surface to an image surface on an optical axis at the telephoto position, a reference symbol fG1 represents a focal length of the first lens unit, a reference symbol fG2 represents a focal length of the second lens unit, and a reference symbol fG3 represents a focal length of the third lens unit.
Another aspect of the present invention pertains to a zoom optical system comprising, in order from an object side: a first lens unit having positive refractive power; a second lens unit having positive refractive power; a third lens unit having negative refractive power; and an aperture stop disposed on an image side of the second lens unit, wherein a magnification is changed from wide-angle position to a telephoto position by moving the lens units toward the object side so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, and wherein the zoom optical system satisfies the following conditions:
0.5 less than LT/fT less than 0.8
0.5 less than fG1/fW less than 1.35
0.2 less than |fG3/fW| less than 0.5
where a reference symbol fW represents a focal length of the zoom optical system at the wide-angle position, a reference symbol fT represents a focal length of the zoom optical system at the telephoto position, a reference symbol LT represents a distance as measured from a most object side surface to an image surface on an optical axis at the telephoto position, a reference symbol fG1 represents a focal length of the first lens unit, and a reference symbol fG3 represents a focal length of the third lens unit.
Another aspect of the present invention pertains to a zoom optical system comprising, in order from an object side: a first lens unit having positive refractive power; a second lens unit having positive refractive power; a third lens unit having negative refractive power; and an aperture stop disposed on an image side of the second lens unit, wherein a magnification is changed from a wide-angle position to a telephoto position by moving the lens units toward the object side so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, wherein the second lens unit comprises a bi-concave lens element disposed on the most object side and at least two positive lens elements, and the second lens unit comprises two lens components or three lens components in all the second lens unit, and wherein the zoom optical system satisfies the following conditions:
0.5 less than LT/fT less than 0.8
0.2 less than |fG3/fW| less than 0.48
where a reference symbol fW represents a focal length of the zoom optical system at the wide-angle position,
a reference symbol fT represents a focal length of the zoom optical system at the telephoto position,
a reference symbol LT represents a distance as measured from a most object side surface to an image surface on an optical axis at the telephoto position, and
a reference symbol fG3 represents a focal length of the third lens unit.
In accordance with another aspect of the present invention, a camera comprises; a photographic system comprising any one of the zoom optical systems described above; and a field stop for determining an image area located on an image side of the zoom optical system.
Furthermore, in accordance with still another aspect of the present invention, a zoom optical system comprises, in order from an object side: a first lens unit having positive refractive power; a second lens unit having positive refractive power; and a third lens unit having negative refractive power, wherein a magnification is changed from a wide-angle position to a telephoto position by moving the lens units toward the object side so as to is widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, wherein the first lens unit consists of, in order from the object side, a negative meniscus lens component having a concave surface facing toward the object side and a bi-convex lens component, and wherein the zoom optical system satisfies the following conditions:
0.5 less than LT/fT less than 0.8
0.5 less than fG1/fW less than 1.5
0.8 less than fG2/fW less than 1.2
0.2 less than |fG3/fW| less than 0.5
where a reference symbol fW represents a focal length of the zoom optical system at the wide-angle position, a reference symbol fT represents a focal length of the zoom optical system at the telephoto position, a reference symbol LT represents a distance as measured from a most object side surface to an image surface on an optical axis at the telephoto position, a reference symbol fG1 represents a focal length of the first lens unit, a reference symbol fG2 represents a focal length of the second lens unit, and a reference symbol fG3 represents a focal length of the third lens unit.
In accordance with another aspect of the present invention, a zoom optical system comprises, in order from an object side: a first lens unit having positive refractive power; a second lens unit having positive refractive power; a third lens unit having negative refractive power; and an aperture stop disposed on an image side of the second lens unit, wherein a magnification is changed from wide-angle position to a telephoto position by moving the lens units toward the object side so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, wherein the first lens unit consists of, in order from the object side, a negative meniscus lens component having a concave surface facing toward the object side and a bi-convex lens component, and wherein the zoom optical system satisfies the following conditions:
0.5 less than LT/fT less than 0.8
0.5 less than fG1/fW less than 1.5
0.2 less than |fG3/fW| less than 0.5
where a reference symbol fW represents a focal length of the zoom optical system at the wide-angle position, a reference symbol fT represents a focal length of the zoom optical system at the telephoto position, a reference symbol LT represents a distance as measured from a most object side surface to an image surface on an optical axis at the telephoto position, a reference symbol fG1 represents a focal length of the first lens unit, and a reference symbol fG3 represents a focal length of the third lens unit.
In accordance with still another aspect of the present invention, a zoom optical system may comprise, in order from an object side: a first lens unit having positive refractive power; a second lens unit having positive refractive power; a third lens unit having negative refractive power; and an aperture stop disposed on an image side of the second lens unit, wherein a magnification is changed from a wide-angle position to a telephoto position by moving the lens units toward the object side so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, wherein the first lens unit consists of, in order from the object side, a negative meniscus lens component having a concave surface facing toward the object side and a bi-convex lens component, wherein the second lens unit comprises a bi-concave lens element disposed on the most object side and at least two positive lens elements, and the second lens unit comprises two lens components or three lens components in all the second lens unit, and wherein the zoom optical system satisfies the following conditions:
0.5 less than LT/fT less than 0.8
0.2 less than |fG3/fW| less than 0.5
where a reference symbol fW represents a focal length of the zoom optical system at the wide-angle position, a reference symbol fT represents a focal length of the zoom optical system at the telephoto position, a reference symbol LT represents a distance as measured from a most object side surface to an image surface on an optical axis at the telephoto position, and a reference symbol fG3 represents a focal length of the third lens unit.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.